The importance of reverse osmosis system pretreatment
The reverse osmosis system includes three parts: pretreatment of raw water, reverse osmosis device, and post-treatment. The reverse osmosis system has its specific requirements for the pretreatment of raw water.
Due to the wide variety of raw waters, the composition is also very complex. For the main process design parameters such as raw water quality and RO system recovery rate, select the appropriate pretreatment process system to reduce the fouling and scaling of RO membrane and prevent RO membrane desalting. The reduction of rate and water production rate, especially for the current scarcity of water sources and deteriorating water quality, the selection of a correct pretreatment system will directly affect the function of the entire water treatment system. As everyone knows. The RO system failed to operate, and most of the cases were caused by imperfect pre-processing system functions. In order to ensure the normal progress of the reverse osmosis process, the raw water must be strictly treated.
Reverse osmosis system pretreatment purpose
1. Remove suspended solids and reduce turbidity
2. Control the growth of microorganisms
3. Inhibition and control of the deposition of slightly soluble salts
4, the inlet water temperature and PH adjustment
5, the removal of organic matter
6. Precipitation control of metal oxides and silicon
Reverse osmosis system pretreatment method
Chemical oxidation
Chemical oxidation treatment is usually a chemical treatment method that uses strong oxidants to decompose organic pollutants in water. At the same time, some oxidants can be used to remove color, taste, smell and iron, and enzyme baths in water. Certain oxidants are also good bactericides.
The chemical oxidant treatment process can be combined with unit treatment processes such as coagulation, filtration, and adsorption to achieve a good treatment effect. The main oxidants commonly used in industrial water treatment are: lv gas, sodium hypochlorite, chlorine dioxide, potassium permanganate, ozone, hydrogen peroxide, and the like.
Drug softening method
The softening of the chemical is a technique in which the hardness of the water is removed by the formation of a poorly soluble compound under the action of a suitable chemical according to the principle of chemical precipitation, and the method of long-shadowing in the water treatment is calcium magnesium ion. The combination of sedimentation, followed by the chlorination of metal ions. The softening of the agent is usually carried out simultaneously with the flocculation, setting or clarification process.
The softening agent for water treatment plants mainly consists of lime, soda ash, toxic sodium, trisodium phosphate, disodium hydrogen phosphate and the like. According to different types of raw water quality, different agents can be combined for treatment. Generally, lime softening method is adopted for water with high hardness and high alkalinity, lime-soda method for water with high hardness and low alkalinity, and lime for water with high alkalinity and negative hardness (that is, total alkalinity is greater than total hardness). - Gypsum method.
Coagulation- flocculation
Coagulation refers to the injection of a certain amount of chemical agents into the water. These chemicals are hydrolyzed in water, and the colloidal particles in the water collide with each other, and electrical neutralization occurs, resulting in adsorption, bridging and net trapping, thereby forming a large The floc particles settle from the water and act to reduce the suspended solids and colloids.
Sometimes when a coagulant alone does not achieve the desired effect, an auxiliary drug may be added to increase the effect of coagulation. This auxiliary agent is called a coagulant. The coagulant itself does not produce the same effect as a coagulant. It can only improve the floc structure and make the floc particles larger, stronger and heavier. Therefore, the use of a coagulant alone does not work well.
Media filtration
Media filtration refers to the use of quartz sand, garnet or anthracite as a medium to pass water under gravity or pressure through a bed composed of these media, while particulate contaminants in the water are blocked by the medium to achieve separation from water. .
Activated carbon adsorption
Activated carbon adsorption is a method in which one or more harmful substances in water are adsorbed on a solid surface by utilizing the porous nature of the activated carbon. Activated carbon adsorption has a good effect on removing organic matter, colloids, microorganisms, residual chlorine, smell and the like in water. At the same time, since activated carbon has a certain reduction effect, it also has a good removal effect on the oxidant in water.
Disc filter
The disc filter is a combination of filter units in parallel, and the filter unit is composed of a set of annular reinforced plastic filter discs with grooves or ribs. When filtering, the sewage enters from the outside, and the rim formed by the groove edge on the adjacent filter disc intercepts the solid matter in the water: when the backwashing water flows from the inside of the annular filter disc to the outside, the pollutants trapped on the aluminum pan will be trapped Rinse off and drain through the drain.
The disc filter has the characteristics of large processing function, stable operation and easy control. At present, most of the domestic pretreatment for ultrafiltration plays a security role of ultrafiltration.
Disc filters can be divided into semi-automatic flushing and fully automatic, the latter being easier to operate with modular control.
Security filtering
In order to prevent the incompletely removed or newly generated suspended particles from entering the reverse osmosis system during the pretreatment, the high pressure pump and the reverse osmosis membrane are protected, and a filter-type security filter is usually provided before the reverse osmosis water is introduced.
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